That RAM is 1.2v from a quick Google. I'd put in the good stick, get to the BIOS and turn off Auto in the voltage setting, and choose 1.2v manually. save settings, then turn it off. Replace good stick with the "bad" stick, turn on, see what happens.
If that didn't work, I'd then inch it up, repeating the process at 1.25v and if need be 1.3v. You're not going to damage anything, and even if you did somehow damage the RAM stick, it's not really working anyway, so nothing lost. Well, you know what I mean.
If that didn't work, then return the RAM, but if it were me I'd like to know. There will be some tolerance to RAM, hence you can have one is working and one not at 1.2v. Maybe 1.21v will do it. Maybe the "good" stick is working will a little less power, maybe your mobo isn't quite hitting 1.2v so setting it manually will do the trick.
I'm simply saying if it was me, I'd try a few more things. And reseating the CPU isn't that tricky, just rebuild the PC on cardboard on the desk, not in the case, it makes messing around a lot easier.
I've found DDR4 and motherboard combinations to be a whole lot more problematic than good old DDR3, but I see you've updated to the latest BIOS so that would have been one of my first questions
Good luck, and if you don't want to try, I completely understand. But then you've purchased a K class CPU, where's the fun in that if you don't want to tinker with overclocking